chapter 8
DESCRIPTION
Chapter 8. Chemical Reactions and Equations. Chemical reactions…. Process by which one or more substances are changed into one or more different substances described by a chemical equation. 4 Signs of a Chemical Reaction:. 1. Evolution of heat and light 2. Production of a gas - PowerPoint PPT PresentationTRANSCRIPT
Chemical reactions….
• Process by which one or more substances are changed into one or more different substances
• described by a chemical equation
4 Signs of a Chemical Reaction:
1. Evolution of heat and light
2. Production of a gas
3. Formation of a precipitate (solid produced as a result of a chem rxn in a sol’n)
4. Color change
Chemical equation
• Represents the identities and relative amounts of the reactants and products in a chemical reaction
• (NH4)2Cr2O7(s) ---> N2(g) + Cr2O3(s) + 4H2O(g)
• Characteristics:– represents the known facts– contains correct formulas for the reactants & products– satisfies the law of conservation of mass (same # and
kind of atoms on both sides of the equation)
(NH4)2Cr2O7(s)---> N2(g) + Cr2O3(s) + 4H2O(g)
• Formula equation: uses symbols/formulas to represent the reactants and products
• Reactants
• products
• coefficient (understood to be “1” if no # appears)
• symbols (p.246)
ammonium dichromate --> nitrogen + chromium(III) oxide + water
• Word equation: (previous ex.)
• only fulfills ONE characteristic of a chem eq (represents the facts)
• 1st step in writing a balanced chemical equation
Steps to write a balanced chemical equation:
1. Write the word equation.
2. Convert the word equation into a formula equation.
3. Include symbols, where known.
4. Balance the equation. NEVER CHANGE A SUBSCRIPT IN BALANCING EQUATIONS!
Solutions of lead(II) nitrate and sodium hydroxide react to produce a lead(II) hydroxide precipitate and an aqueous solution of sodium nitrate.
Lithium reacts with a hydrochloric acid solution to produce an aqueous solution
of lithium chloride and hydrogen.
In the presence of an electrical current, sodium hydroxide can be produced from the reaction of a sodium chloride solution with water. Hydrogen and chlorine gases are the other products.
Aluminum sulfate is produced when aluminum hydroxide reacts with sulfuric acid. Water is the other product.